Process and apparatus for the continuously densifying nonwoven webs

ABSTRACT

This invention relates to a process and apparatus for the production of a web of fiber fleece densified by heat shrinkage, which process comprises exposing the moving web to heat beginning simultaneously at opposite points on each edge of the web and continuing with time delay in the direction perpendicular to the web axis.

United States Patent 1 Porrmann et al.

[4 1 July 24, 1973 PROCESS AND APPARATUS FOR THE CONTINUOUSLY DENSIFYING NONWOVEN WEBS [75] Inventors: Herbert Porrmann, Konigshofen;

Ludwig Klenk, Hallgarten; Manfred Liiffler, Wiesbaden-Biebrich, all of Germany [73] Assignee: Kalle Aktiengesellschait,

Wiesbaden-Biebrick, Germany [22] Filed: Sept. 14, 1970 [21] Appl. No.: 71,686

[30] Foreign Application Priority Data Sept. 17, 1969 Germany P 19 47 058.7

[52] U.S. Cl. 26/l8.5 [51] Int. Cl D06c 7/00, D060 29/00 [58] Field of Search 26/1, 18.5; 34/1 [56] References Cited UNITED STATES PATENTS 3,235,931 2/1966 Bruckner 26/1 2,629,162 2/1953 Peck 26/1 3,471,682 10/1969 Hisey et a1... 34/1 X 2,343,351 3/1944 Wedler... 26/] UK FOREIGN PATENTS OR APPLICATIONS 1,163,138 9/1969 Great Britain... 26/l8.5 1,460,504 3/1969 Germany 26/18.5

Primary Examiner-Robert R. Mackey AttorneyJames E. Bryan [57] ABSTRACT This invention relates to a process and apparatus for the production of a web of fiber fleece densified by heat shrinkage, which process comprises exposing the moving web to heat beginning simultaneously at opposite points on each edge of the web and continuing with time delay in the direction perpendicular to the web axis.

4 Claims, 5 Drawing Figures PAIENTEDJULZMSH SHEET 1 0F 2 2 mvnmons HERBERT RMANN LUDWIG K NK MANFRED .LOFFLER BY W n'ronmzv PROCESS AND APPARATUS FOR THE CONTINUOUSLY DENSIFYING NONWOVEN WEBS The present invention relates to a process for the continuous production of a web of fiber fleece densified by heat shrinkage which has a substantially structureless surface and a substantially uniform density over its width. The invention further relates to a fleece web produced according to the process and to an apparatus for the performance of the process.

According to known processes, densification of a fiber fleece made from heat shrinkable fibers is performed in a manner such that, within a certain zone, the web is exposed to heat simultaneously over the entire area thereof, whereby area shrinkage of the fleece is effected in this zone. Shrinkage in the longitudinal direction is determined by the feed and draw-off speeds of the conveying elements mounted in front of and behind the aforementioned zone. Shrinkage in the transverse direction generally is unrestrained, i.e. the width of the shrunk web cannot be exactly predetermined.

The introduction of a fleece web of which at least a portion of the fibers is capable of being shortened by the action of heat is accompanied by contraction of the fibers occurring immediately upon the action of heat. Since in the case of fibers of readily crystallizable highpolymers the action of heat also causes crystallization, it is usually absolutely necessary to shrink at a high rate in order to prevent crystallization. For geometrical reasons there are differences in the path lengths over the width of the fleece web which must be covered by the individual web points during shrinkage of the web. Tension differences are caused thereby which become noticeable by structure and density differences. These differences impart an unpleasant appearance to the fleece material and often make it useless for further processing into high-quality goods. It is also known to fold or pleat the shrinkable web of fleece made from heat shrinkable synthetic fibers by suitable devices, eg by one or more toothed bars or interlocking rollers, in such a manner that the width of the pleated shrinkable web of fleece material, which is projected onto a plane parallel to the web, corresponds to the width of the shrunk web. It is thus possible to minimize the path differences during shrinkage. It is of disadvantage, however, that the curvature stresses at the crease bends are marked in the fleece webs so that a streaky appearance of the web is an unavoidable consequence.

The path length differences occurring during shrinkage increase towards the lateral zones of the web according to a parabolic function as shown in the accompanying drawings, in which:

FIG. 1 is a diagrammatic view of the shrinking process of a planar fleece web,

FIG. 2 is a diagrammatic plan view of a specific embodiment for the performance of theprocess of the invention, in which the heating element is formed by a plurality of individual heating elements arranged in one plane and side by side and one behind the other,

FIG. 2a is a diagrammatic side elevation of FIG. 2,

FIG. 3 is a plan view and shows another specific embodiment for the performance of the process of the invention, in which the heating element is formed by a tubular system, and

FIG. 3a is a diagrammatic side elevation of FIG. 3.

. According to FIG. 1, x is the distance of a web point of the shrinkable web from the center line, )I the ratio of the width b of the shrunk web to the width b, of the shrinkable web, and I the shortest shrinkage path in the middle of the web. The ath len ths y are calculated according to y /1 [x (l )r)] or the path length differences A according to A y {W I.

It easily can be seen that the path length differences become smaller as the shortest path 1 available for the shrinkage process increases and the smaller the ratio A It is known that, according to these simple considerations, attempts have been made to compensate the path length differences by deflections of the shrinkable web from the plane of the web. It has been suggested to convert the web of fleece material made of heatshrinkable fibers into a tube and to perform shrinkage on an internal mandrel exactly determining the shrinkage degree and, after shrinkage, to axially sever and collapse the shrunk tube. This process solves the problem of shrinking a fleece web with equal path lengths in an ideal manner, but it can be performed only with expensive apparatus since every size of tube requires a corresponding internal mandrel in dependence upon the desired shrinkage ratio.

The present invention provides a continuous process for the densification of a fleece material by heat shrinkage, which overcomes the drawbacks of the known processes, which produces a shrunk fleece web having the required quality characteristics, and which can be performed without expensive apparatus.

In the present process for the production of a web of fleece material densifled by heat shrinkage, the web is advanced in the longitudinal direction and exposed to heat, starting simultaneously at opposite points on each web edge and continuing with time delay in the direction perpendicular to the web axis.

It is particularly advantageous to cool the zones of the fleece web which are not exposed to heat in order to prevent uncontrolled and premature heating of these zones.

The term web" or fleece web means an unwoven, planar, fibrous sheet material of substantially uniform thickness over its entire length. The web edge means the lateral border of the web.

An unwoven fibrous sheet material means a layer of fibers arranged loosely either randomly or in a preferred direction. Fiber fleece layers mechanically densified by needling are included in the definition of unwoven fibrous sheet materials of loosely arranged fibers.

The web direction is the direction of travel of the web during the performance of the process.

The usually immediately occurring contraction of the fibers upon the action of heat is called fiber shrinkage.

Area shrinkage of the fleece web upon the action of heat thereon is the consequence of the simultaneously occurring shortening of all heat shrinkable fibers of the fleece under the stated conditions. Area shrinkage is manifested by a dimensional change of the web. A significant physical feature is the change of the weight per unit of area of the web, which results from heat shrinkage.

A heat shrinkable fiber is a fiber which, upon the action of heat transfer media, e.g. warm gases or warm liquids, is shortened by at least 5 per cent of its original length. Particularly suitable are those heat shrinkable fibers the length shortening of which is more than 40 per cent of the original length upon the action of heat transfer media.

Suitable fiber fleeces for the performance of the process are those formed from synthetic fibers, particularly needled fleeces from synthetic fibers, of which a fiber portion of at least per cent by weight of the total quantity of fibers consists of heat shrinkable fibers. Particularly suitable, however, are those fiber fleeces which have a portion of more than per cent by weight of heat shrinkable synthetic fibers. A suitable fiber fleece also may consist of mixtures of at least two chemically identical synthetic fibers in which case it is possible that chemically identical fibers of which one part is heat shrinkable and the other one non-heat shrinkable are employed simultaneously. A fleece consisting of heat shrinkable fibers and predensified by needling has a weight in the range from to 500 g/m particularly in the range of to 300 g/m The fleece has a needling density in the range from 100 to 600 stitches/cm particularly in the range from 300 to the 500 stitches/cm.

A fleece needled with a stitch density in the range from 300 to 500 stitches/cmand consiting of fibers of the kind described with a portion of heat shrinkable fibers in the range of 30 to 50 per cent by weight, calculated on the total weight of fibers, has an area shrinkage in the range of 30 to 60 per cent.

Heat-shrunk needled fleeces of the above kind have a weight in the range of 71.5 to 1,250 g/m, particularly in the range of to 720 g/m The above-mentioned fleeces consist of fibers having a range of 0.8 to 3 denier, particularly in the range of 1.2 to 2.5 denier.

Provided the fleece consists exclusively of heat shrinkable fibers, fibers of crystalline or partially crystalline synthetic materials are suitable, eg of polyethylene, polypropylene, polyvinylidene chloride, polyacrylonitrile, and polyamide, particularly, however, of polyethylene terephthalate.

Suitable non-heat shrinkable fibers of the fleece are, in principle, all natural and synthetic fibers, eg those of natural or regenerated cellulose or those of synthetic high-polymers.

Particularly suitable non-heat shrinkable fibers are those of synthetic high-polymers, such as polyamide, polyethylene ter'ephthalate, or polyacrylonitrile.

In the performance of the process of the invention, the fleece web is conveyed through the roll gaps of two coaxially arranged pairs of-rolls. The fleeces used for the performance of the process of the invention have an elasticity in the longitudinal direction in the range of l to 10 per cent. Particularly suitable are those which have an elasticity in the longitudinal direction of more than 3 per cent. The elasticity of the fleece means that portion of the extension upon tensile stress which completely disappears after removal of the stress.

The term section means an imaginary rectangular zone of the steadily advancing web, which is limited by symmetrical web edges of equal lengths and by parallel lines perpendicular thereto and the lengths of which correspond to the web width. The section means the section of the steadily advanced web which is determined by the distance of the axes of two parallel pairs of rolls, the one being the pair of inlet rolls and the other one being the pair of outlet rolls, and by the edges of the fleece web.

The effective length of this section is by (r /2) (R /2) smaller than the above-mentioned area, R being the radius of the inlet rolls and R the radius of the outlet rolls.

The process of the invention is performed in a manner such that a fiber fleece web, with at least one portion of the fibers being heat shrinkable, is continuously and frictionally conveyed in the web direction through the gap of the pair of inlet rolls and then in the same plane in a manner such that the longitudinal axis of the web coincides with the axis of symmetry of the heating elements arranged either on one side or, preferably, on both sides of and parallel to the plane of the roll gaps and into the gap of a pair of outlet rolls arranged coaxially to and at a distance from the pair of inlet rolls and out of it.

The number of revolutions of the two inlet rolls is greater than the number of revolutions of the two outlet rolls. Both rolls of each pair of rolls have the same number of revolutions. The rollers of each pair of rolls are counter-rotating. The distance of the two pairs of rolls from one another substantially corresponds to the length of the fleece section within which shrinkage is effected in accordance with the invention.

In the case of preferably bilaterally arranged heating elements, these are arranged symmetrically and are so positioned that the heating area of the heating element or elements directed to the aforementioned plane is laterally limited by two parallel straight lines the length of which substantially corresponds to the distance of the two pairs of rolls, the distance of the two straight parallel lines substantially corresponding to the length of the pairs of rolls. The base line of the heating element is a straight line of a length substantially corresponding to the width of the rolls and extending parallel to and at a small distance from the outlet rolls. The heating element is further limited by two diverging straight lines, each extending from the end of one of the lateral edges which is adjacent the pair of inlet rolls at the same angle with respect to the lateral edges of the heating element, the angle being such that the diverging straight lines, also designated as inside edges of the heating element, approach one another and meet before reaching the base line of the heating element.

In a preferred embodiment of the invention, in the zone between the two pairs of rolls in the plane of the heating element with a pentagonal effective heating area, or parallel and beneath this plane, there is mounted a cooling element with a triangular effective cooling area directed to the plane of the roll gaps, the base line of the triangle substantially corresponding to the length of the inlet rolls and the lateral edges of equal length of the triangular cooling element substantially corresponding to the inside edges of the heating element and forming an angle with one another which corresponds to the angle formed by the inside edges of the heating element. The lateral edges of equal length of the triangle form an angle the apex of which is directed towards the pair of outlet rolls. The effective area of the heating element and the effective area of the cooling element represent a rectangular effective area since both elements are arranged to one another in such a manner that the inside edges of the effective heating area extend at the angle sides of the effective area of the cooling element.

In a preferred embodiment with one heating element arranged at each side of the plane of the roll gaps, there are mounted cooling elements at both sides of the plane of the roll gaps, which are congruent and arranged with respect to the heating elements as described above.

Between the gaps of the two pairs of rolls, the plane of the fleece web is parallel to the plane of the heating element or cooling element. The distance of the surface of the fleece web from the surface of the heating or cooling element is in the range of to 500 mm, particularly in the range of 10 to 200 mm. The shortest distance between the facing surfaces of the pair of inlet rolls and the pair of outlet rolls is in the range of 200 to 4,000 mm, particularly in the range of 200 to 2,000 mm. The length of the rolls is in the range of 200 to 3,000 mm, particularly in the range of 200 to 2,000

The distance of the base line of the cooling element of a triangular surface from the roll surface of the pair of inlet rolls is in the range of 1 to 300 mm.

The boundary edge of the heating element which is parallel to the surface of the rolls of the pair of outlet rolls, also designated as the base line of the heating element, has a distance in the range of l to 1,000 mm therefrom.

The distance of the point of intersection of the inside edges of the heating element from the base line thereof is in the range of 200 to 3,998 mm.

The number of revolutions of the rolls of the pair of inlet rolls is in the range of 1 to 50 revolutions per minute, particularly in the range of 3 to 35 revolutions per minute, whereas the number of revolutions of the rolls of thepair of outlet rolls is in the range of 0.5 to 25 revolutions per minute, particularly in the range of 1.5 to 17.5 revolutions per minute.

The fleece web leaves the pair of outlet rolls at a speed in the range of 0.5 to 20 m/minute, particularly at a speed in the range of l to 10 m/minute. For the performance of the process, there is used a fleece web of a width substantially corresponding to the width of the pairs of rolls.

Advantageously, the heating element consists of a heat-radiant ceramic body or of a plurality of such bodies which together form the described area of the heating element. The heating element, however, also may consist of a system of tubes closely adjacent one another in one plane and carrying a heat-transfer medium. The tubes advantageously have a plurality of uniformly distributed spray nozzles directed towards the surface of the fleece web and substantially equidistant from one another. The apertures thereof are substantially in one plane. The heat-transfer medium leaves the nozzles.'The plane in which the apertures are is the planar heating area.

Suitable heat-transfer media are hot water or hot gases. In the case of heating elements with the heattransfer medium leaving spray nozzles, steam is a particularly suitable heat-transfer medium.

The heating element also may consist of a planar arrangement of a plurality of electrically heated devices.

The cooling element consists of a hollow body or a container with a planar triangular surface directed towards the fleece. The hollow body or the container contains the cooling agent, advantageously a liquid cooling agent, particularly water of a temperature in the range of 0 to 25 C.

The heat-transfer media used for heating a heating element formed by tubes have a temperature in the range from 60 to 150 C., particularly in the range of to C. If the heating elements are heated electrically, the electric energy is of such an intensity that the heat coming from the heating elements heats the fiber fleece to a temperature sufficient to effect longitudinal shortening of the heat shrinkable fibers. This effect occurs if the fiber fleece is exposed to a temperature in the range from 60 to C., particularly in the range of 70 to 120 C.

Due to the steady movement of the web through a heating zone and a cooling zone of the described design, shrinkage in the web occurs continuously with a time delay from the web edge to the center of the web. This is easily understandable when imagining a narrow rectangular web section of the length of the web width, which, when leaving the gap of the inlet rolls is exposed to the action of heat of the heating element with its zones near the longitudinal edges, whereas no shrinkage yet occurs in the other zones of this strip since these zones are still under the influence of the cooling device. With the continuing movement of the section in the web direction, the zones extending from the lateral edges towards the web axis and coming under the action of heat become larger and larger. 1n the last phase of the travel of the imaginary section through the heating zone, also that zone of the section which is very near the web axis comes under the action of heat. In this phase of the process, heat shrinkage is uniform over the entire width of the imaginary section.

The apparatus for the performance of the process of the invention comprises two pairs of rolls with axes parallel to one another, the one pair of rolls serving as inlet rolls and the second pair of rolls as outlet rolls of the apparatus. The roll gaps of the two pairs of rolls are in one plane and the pairs of rolls are distanced from one another. In the zone between the two pairs of rolls and parallel to the plane of the roll gaps, there are arranged at one or both sides of this plane a heating element with a substantially planar effective heating area facing the plane of the roll gaps, and a cooling element with a planar effective cooling area similarly facing the plane of the roll gaps and mounted in the same plane as the effective heating area or parallel thereto, but at a smaller distance from the plane of the roll gaps than the heating area. With one heating element and one cooling element on each side of the plane of the roll gaps, the heating elements as well as the cooling elements are arranged symmetrically with respect to one another.

The heating element has a pentagonal area and the cooling element has the form of an isosceles triangle. The surfaces of a heating element and a cooling element facing the plane of the roll gaps preferably are mounted in planes parallel to one another. The same applies to heating and cooling elements arranged on both sides of the plane of the roll gaps.

The cooling element with a cooling area in the form of an isosceles triangle, of which the base line substantially corresponds to the length of the inlet rolls and the sides of equal length substantially correspond to the length of the inside edges'of the heating element and form an angle with one another which corresponds to the angle formed by the inside edges of the heating element, forms a rectangular area together with the heating element. This area is formed from the aforementioned parts in such a manner that an inside edge of a heating element is parallel to a side of a cooling element and closely adjacent thereto. For the preferred arrangement of heating and cooling elements, the term rectangular area applies when viewing these two areas from the plane of the roll gaps.

The axes of symmetry of the heating and cooling elements are in a plane perpendicular to the axis of symmetry of the plane of the roll gaps.

The effective pentagonal heating area and the triangular cooling area are summarized under the term treating area."

The heating element preferably has such a form that the angle formed by the lateral edge and the inside edge is so selected that, on the one hand, sufficient time delay of the shrinkage of the fleece from the edge of the web towards the center occurs during the travel through the heating zone and, on the other hand, however, that the fleece zones closely adjacent the web axis are completely shrunk during the travel of the fleece through the zone between the two pairs of rolls. Considering the elasticity of the fleece, the size of the angle is so selected that the maximum path length difference or tension difference in the fleece section between a feeding element and a draw-off element of the apparatus does not involve permanent deformation of the fleece web.

The apparatus for the performance of the process of the invention includes a pair of inlet rolls and, distanced therefrom, a pair of outlet rolls, the roll gaps of which are in one plane, as well as of heating and cooling elements arranged on one side or on both sides of this plane. The effective heating area or areas are pentagonal and the effective cooling area or areas are in the form of an isosceles triangle with the apex directed towards the pair of outlet rolls, the heating and cooling areas of the elements complementing to form a rectangular treating area and the axes of symmetry of the heating and cooling areas being in a plane perpendicular to the axis of symmetry of the plane of the roll gaps.

Referring to FIG. 1, numeral 1 indicates the shrinkable fleece web, numeral 6 the completely shrunk portion of the fleece web and numeral 9 that portion of the web in which shrinkage of the web occurs, b indicates the width of the shrinkable web and b the width of the shrunk fleece web, x is the distance of a web point of the shrinkable web from the center line of the web, A is the ratio of the width of the shrunk web to the width of the shrinkable web, I is the shortest shrinkage path in the middle of the web, and y means the path length of a web point.

in FIG. 2, numeral 1 indicates the shrinkable fleece web, numeral 6 the shrunk fleece web, numeral 2 a roll of the pair of inlet rolls, and numeral designates a roll of the pair of outlet rolls. Numeral 3 indicates a rectangular heating element component, a plurality of heating element components staggered and arranged behind one another forming the entire heating element. Numeral 4 indicates the cooling element.

In FIG. 2a, numerals I, 2, 3, 4, 5, and 6 have the same meanings as in FIG. 2.

In FIG. 3, numerals I, 2, 4, 5, and 6 have the same meanings as in FIG. 2. Numeral 3a indicates a heating element in the form of a tube having several hair-pin bends, which has a plurality of equidistant spray nozzles 3b directed towards the fleece surface. The apertures of the spray nozzles are substantially in one plane.

In FIG. 3a, numerals 1, 2, 3a, 4, 5, and 6 have the same meanings as in FIG. 3, numeral 3b indicates a spray nozzle.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. An apparatus for the densification of a non-woven web of fiber fleece by heat shrinkage which comprises a pair of feed roll means, a pair of discharge roll means spaced therefrom to define a treating zone between said feed and discharge roll means, the web being unconfined laterally within the zone, said feed roll means being driven faster than said discharge roll means, heating and cooling means arranged on at least one side of the plane of the treating zone, the effective heating area being pentagonal in shape and the effective cooling area being in the shape of an isosceles triangle with the apex pointing towards the discharge roll means, the heating and cooling areas complementing to form a rectangular treating area, whereby the moving web is exposed to heat beginning simultaneously at opposite points on each edge of the web and continuing with time delay in the direction perpendicular to the web axis to effect substantially uniform shrinkage and densification of the web over its width in the treating zone.

2. An apparatus according to claim 1 in which the axes of symmetry of the heating and cooling areas are in a plane normal to the axis of symmetry of the plane of the roll gaps.

3. An apparatus according to claim 1 in which the heating means comprises a plurality of spray nozzles uniformly distributed over the heating area thereof.

4. A process for the continuous production of a web of non-woven fiber fleece substantially uniformly densified by heat shrinkage which comprises continuously overfeeding said web through a heat treating zone, and exposing the moving web to heat beginning simultaneously at opposite points on each edge of the web and continuing with time delay in the direction perpendicular to the web axis to the center of the web while clearly confining the perimeters of the area of heat application and while maintaining said web free of lateral restraint. 

1. An apparatus for the densification of a non-woven web of fiber fleece by heat shrinkage which comprises a pair of feed roll means, a pair of discharge roll means spaced therefrom to define a treating zone between said feed and discharge roll means, the web being unconfined laterally within the zone, said feed roll means being driven faster than said discharge roll means, heating and cooling means arranged on at least one side of the plane of the treating zone, the effective heating area being pentagonal in shape and the effective cooling area being in the shape of an isosceles triangle with the apex pointing towards the discharge roll means, the heating and cooling areas complementing to form a rectangular treating area, whereby the moving web is exposed to heat beginning simultaneously at opposite points on each edge of the web and continuing with time delay in the direction perpendicular to the web axis to effect substantially uniform shrinkage and densification of the web over its width in the treating zone.
 2. An apparatus according to claim 1 in which the axes of symmetry of the heating and cooling areas are in a plane normal to the axis of symmetry of the plane of the roll gaps.
 3. An apparatus according to claim 1 in which the heating means comprises a plurality of spray nozzles uniformly distributed over the heating area thereof.
 4. A process for the continuous production of a web of non-woven fiber fleece substantially uniformly densified by heat shrinkage which comprises continuously overfeeding said web through a heat treating zone, and exposing the moving web to heat beginning simultaneously at opposite points on each edge of the web and continuing with time delay in the direction perpendicular to the web axis to the centEr of the web while clearly confining the perimeters of the area of heat application and while maintaining said web free of lateral restraint. 